1. Field of the Invention
The present invention relates generally to switch-mode power conversion, and more specifically, to a passive shoot-through protection circuit for active switches in clamp-mode topologies.
2. Related Art
Switch-mode power converters are widely used in power processing applications to convert an input voltage or current source into a specified output voltage or current. A basic topology configuration employed in many switch-mode converters is a clamp-mode topology, which generally includes at least one type of clamping device (also referred to as an xe2x80x9cactive clamp,xe2x80x9d a xe2x80x9cCarsten clamp,xe2x80x9d or a xe2x80x9cPolykarpov clampxe2x80x9d). The clamping device, in particular, is typically a switching device (auxiliary switch) connected in series with a capacitor. Generally, the clamping device transfers or recycles stored energy from the capacitor to a transformer(s) winding(s) during a converter""s off period. For example, at a time after a primary switch of the converter is inactive (off period), the auxiliary switch is turned-on (activated), thus transferring any stored energy between the clamping device""s capacitor and the transformer(s) winding(s).
A primary requirement in most clamp-mode topologies is that there be no overlap between the primary switch and the auxiliary switch, because even a brief overlap of conduction period of the two switches, (typically on the same side of the transformer), can result in substantial shoot-through currents (short circuits) and cause catastrophic circuit damage, such as a burned out switch. As a result designers have been required to include delays between the turn-off of one switch, and turn-on of the other, see, i.e., U.S. Pat. No. 4,441,146, issued Apr. 3, 1984 to Vinciarelli, (the ""146 patent) (requirement to avoid an overlap between switches) and U.S. Pat. No. 5,331,533, issued Jul. 19, 1994, to Smith (the ""533 patent) both incorporated herein in their entirety.
Sometimes when the delay between the auxiliary switch and the primary switch is designed to a minimum, however, inadvertent simultaneous conduction of both switches can occur due to operational corruption and/or converter imperfections, such as, manufacturing variances between component values of the converter. These variances can create brief timing irregularities and can cause an overlap of conduction between the primary and auxiliary switches. Ensuring that there is a large enough delay through testing and design is costly and increases circuit complexity of converters.
Therefore, what is needed is a way to protect constituent components of a clamp-mode converter when there is simultaneous conduction of the primary switch and the clamping switch.
The present invention is directed to an impedance network for passive shoot-through protection of active switches in clamp-mode topologies. In one exemplary embodiment a switch-mode converter, includes: a primary switch; an auxiliary switch coupled in series with a capacitor; and an impedance network, coupled to the primary switch and the auxiliary switch; configured to limit current during simultaneous conduction of the primary and auxiliary switches.